The present invention relates to a semiconductor device having a wiring layer of damascene structure and a method for manufacturing the semiconductor device. More specifically, the present invention relates to a damascene technique that is very useful for miniaturizing a semiconductor device and decreasing the size of a chip.
Miniaturization of semiconductor devices has recently been advanced to make a wiring layer difficult to form by conventional RIE (Reactive Ion Etching). This difficulty is ascribed to difficulties in improvement of yields and flattening when a conductive film is microfabricated by the RIE. As a technique of resolving this problem, a wiring layer of damascene structure (referred to as a damascene wiring layer) has been known conventionally.
FIGS. 9A to 9C schematically show a process of manufacturing a prior art semiconductor device having a damascene wiring layer (a method of forming a damascene wiring layer).
First, an interlayer insulation film 101 is formed on a semiconductor substrate 100 and a wiring pattern groove 103 is formed in the interlayer insulation film 101 by known lithography and RIE, as shown in FIG. 9A. Then, a barrier metal film 105 is deposited on the entire surface of the resultant structure, as illustrated in FIG. 9B. A conductive film 107 is deposited on the barrier metal layer 105 to completely fill the wiring pattern groove 103.
After that, the surface of the resultant structure is flattened by CMP (chemical mechanical polishing), as shown in FIG. 9C. A damascene wiring layer 109 is thus obtained in which the conductive film 107 and the barrier metal film 105 are buried into the wiring pattern groove 103.
A multilevel wiring layer can easily be formed if the above-described process is repeated.
In forming a damascene wiring layer, however, it was necessary to deposit titanium nitride (TiN), niobium (Nb) and the like as a barrier metal film 105 in order to bury tungsten (W), aluminum (Al) and the like in the wiring pattern groove 103 as the conductive film 107. The barrier metal film 105 increases in adhesion to the interlayer insulation film 101 of tungsten (W) and serves as a glue layer or a barrier layer in reflowing of aluminum (Al).
The resistivity of the barrier metal film 105 is generally higher than that of the conductive film 107. Therefore, the prior art semiconductor device described above had a problem that the resistance of the damascene wiring layer was higher than a wiring layer formed by the RIE method (referred to as an RIE wiring layer hereinafter).
FIGS. 10A and 10B illustrate a damascene wiring layer and an RIE wiring layer having the same line width L for purposes of comparison.
In the damascene wiring layer 109 shown in FIG. 10A, the barrier metal film 105 is formed on each sidewall of the conductive film 107. Thus, the width L′ of the conductive film 107 is smaller than the line width L of the damascene wiring layer 109 by two times (2b) the thickness of the barrier metal film 105 (L′=L−2b<L). In the RIE wiring layer 201 shown in FIG. 10B, the width L′ of the conductive film 107 is equal to the line width L of the RIE wiring layer 201 (L′=L). In other words, the cross-sectional area (volume) of the conductive film 107 in the damascene wiring layer 109 is relatively smaller than that in the RIE wiring layer 201.
The thickness (b) of the barrier metal film 105 is determined appropriately to serve as a glue layer for forming the conductive film 107, to secure adhesion enough to form the film 107, or to obtain good characteristics of contact with the interlayer insulation film 101. In short, the barrier metal film 105 having a given thickness or more is indispensable for forming the damascene wiring layer 109.
If the damascene technique is applied to the formation of wiring, the volume of the barrier metal film in the wiring increases relatively as a semiconductor device decreases in size. As a result, the cross-sectional area of the conductive film decreases and thus the resistance of the wiring increases, or a so-called thin-wire effect is problematic.
The above barrier metal film has the problems that it hardly contributes to a reduction in wiring resistance and narrows a distance between adjacent wiring layers and increases the capacitance between them.
The prior art damascene wiring layer has the problems that the wiring resistance increases and the wiring-to-wiring capacitance increases though the conductive film is improved in yield and easily flattened and the semiconductor device can sufficiently be miniaturized.